I think you've got a minority opinion calling crystals "alive," although it does jibe with one definition of life that I heard: "any self-sustaining system that reduces internal entropy."
> Cairns-Smith found a more eager audience in science journalists and the popular press. Other scientists showed interest, too: the evolutionary biologist and writer Richard Dawkins discussed the crystals-as-genes hypothesis in his 1986 book The Blind Watchmaker.
[...]
> His aim was to find a system much simpler than modern life, but which had some of the crucial properties of a living system. He found an answer in an unlikely place: clays.
My favorite version of this classifies life as an exotic phase of matter in the sense of other exotic phases like Bose-Einstein condensates, etc.
Life is a phase of matter in which the dynamics of information and Turing-complete computation overcome the ordinary dynamics of matter and energy. I am not aware of who originated this idea, but I heard it from Christoph Adami (a researcher in evolutionary information theory). I also recall someone at a conference proposing the term "Turium," for "Turing-complete phase of matter."
Earth just happens to have an environment that contains a large abundance of this phase of matter, much like how stars are full of plasma etc.
How is this model useful? It certainly moves away from our domain knowledge and paints a new picture that is considerably more fuzzy than the old one. What do you gain by considering life in such way?
Side note: computation seems like a wrong term, because it's not about counting/calculating/determining any abstract value, is it? A Turing-complete mechanism maybe?
I find the idea of it as a phase of matter very conceptually elegant in that it neatly classifies life as a unique but still physical phenomenon. Nevertheless I agree with you that the details of the definition are hard to pin down.
Of course I have yet to see an attempted definition of life that isn’t a little squirrely or that isn’t just a list of criteria taken from the one example we have.
While obviously crystals are not alive, they satisfy more careless definitions of life that were sometimes encountered, i.e., when put in a "nutritive" solution, they are able to grow and reproduce themselves.
This is just wrong (as you say, careless). The criteria is "metabolism", not growth and reproduction. Similarly, viruses are not alive although they can reproduce. Interestingly, there are some highly parasitic organisms with limited ability to metabolize, that is, they have lost their genes and instead depend on their host organism (but I think all those examples still have some level of metabolic capability).
I don't really know what "metabolism" means, abstractly. I am deader than a virus without chloroplasts existing elsewhere. Viruses need a host for the productive bit, I had food for the non-reproductive bit. Viruses don't break down fast enough compared to their abundance to cause extinction, so why fault them for optimizing?
People commonly theorize that virus came from rump parasitic cells. I wouldn't be surprised if at some point a huge virus with a membrane accidentally picked up enough stuff to become a cell again. To go back to chloroplasts again, it would be like how brown algae is an ex-heterotroph.
There used to be a hypothesis that DNA originated in viruses and that the three branches of life (archea, bacteria and eukaryota) evolved when three different DNA viruses encountered preexisting RNA-based cells. (https://www.pnas.org/content/103/10/3669)
Nowadays however it is more widely believed that eukaryota descend from archea, but anyway it's pretty much a given that viruses are not and have never been alive. And while the opposite has happened, gene transfer usually goes from viruses to cells, endowing them with new abilities, more than the opposite direction.
Metabolism has two parts: Catabolism breaks down complex molecules into smaller building block molecules - think proteins -> amino acids. Then anabolism uses those building blocks to build up larger molecules for growth and maintenance. Crystals don't do the catabolism part.
Looks like cell's phospholipid bilayer is anabolized just like an "endothermic" crystal : no need to cross a potential barrier (and releases energy instead of consuming it)?
On the other hand, other forms of anabolism require crossing an energy barrier (and consumes energy) ?
While catabolysm is the inverse operation : crosses a barrier, but releases energy?
The formation/destruction of "exothermic" crystals like dissolution of Sodium Hydroxide if put in contact with water is I guess similar to above two reactions ? (Or better example: explosives)
> People commonly theorize that virus came from rump parasitic cells.
I have an alternate theory, that I've never seen articulated elsewhere: Viruses might be inter-microbial biochemical warfare gone wild; Among primitive and not-particularly robust cells, one competitive strategy might be to package toxins or other disruptive molecules into capsids that cleverly get past the 'enemy' cell membrane, perhaps aimed simply at disrupting the initially brittle reproductive process. Packaging random genes in with these capsids would be the beginning of the Horizontal Gene Transfer function that viruses perform in the ecosystem. A refinement would be to add in the specific genes for producing capsids as a deliverable so a subverted 'enemy' then takes out several neighbors (but 2nd gen capsids don't have to necessarily contain the same genes in order to accomplish their 'mission', or even be entirely identical to the 1st gen, as long as they work). A further refinement would be increasing fidelity, and packaging the responsible genes into the 2nd gen capsids produced by subverted cells so the 'weapon' can spread exponentially.
And voila, the 'weapon' has now escaped the originating organism and can evolve independently parasitizing the target. Each incremental step can at least hypothetically provide an evolutionary advantage so the whole thing doesn't have to spring forth fully formed.
Depending on how widespread variants of the original strategy were, viruses might have independently emerged more than once.
If I'm right, we ought to still be able to find cells that attack or suppress competitors with capsid-like molecules that don't particularly resemble existing virus lineages, possibly containing non-genetic payloads of various sorts.
We might also find bacteriophage endoviruses that as their 2nd stage only produce capsids sans-genes or that otherwise aren't identical to the endovirus, or ones that aren't very good at packaging up the correct genes, or that are much better at disrupting cell reproduction than hijacking it, or that the subsequent copies are only low-fidelity ones that can similarly penetrate the host but not spread any further; basically any indicators that the mechanisms for penetration of the membrane, attacking the cell, and even for making poor 2nd gen copies, have been evolving longer than capabilities only needed for indefinitely repeated copying, retransmission, and reinfection.
I suspect though that the oldest reconstructible endoviruses will no longer be capable of penetrating current members of their host cohort, which tells us little about the virus itself, but may offer clues about whatever ancestral cells were still prone to infection were like.
Viruses need a host environment to replicate. Fish need water and plant life or other fish to replicate. Algae needs nutrients to replicate. Every lifeform can only exist in some host environment. Viruses simply happen to have biological host environments, right?
I would say neither. Your body is a colony, like an ant colony or bee colony. In all instances, most individuals can't start a colony of their own but it's limited to a set of queens/gametic cells.
As for shooting into the head, some multicellular life forms can actually heal from that. From planaria you can remove any part of their bodies, it will grow back. Shooting into an ant colony won't do much harm to them either, nor is removing the branch of a tree. It's only a property of animals I'd say who have given up this property (for the most part) in exchange for more complex metabolic systems. (heart, nervous system, etc)
In fact, for quite a few fish they do, ditto amphibians and insects too.
Mammals are the exception here, there the environment for replication is an integral part of the body of the parent. But in all those other cases, including, technically, marsupials it isn't.
Just because it happens outside the ‘parents’ body doesn’t mean the environment does it anymore than a mother being only a filter around the womb and the environment.
An egg is a complex life that can reproduce the whole organism (and actually with energy stored INSIDE, that’s why they are great nutritios value for others)
I think even under that definition they don't truly reproduce and still aren't really life -- they don't create the same material they arise from for example (so not allowing for additional crystals to form). A non-renewing source of the material has a maximum amount of crystal that can grow, I would imagine. This is different than something like a virus, which carries the instructs to replicate itself and the ability to travel to new hosts to create more of itself (and still isn't really considered alive).
> A non-renewing source of the material has a maximum amount of crystal that can grow
So any biosphere that fails to escape its looming red giant was never alive?
I'm not a "all abstractions leak" type of person, so I will choose my definitions very carefully, with funny choices about clays, crystals, virus, etc. as an acceptable causality.
Crystals don’t reduce their internal entropy. They grow only on the interface with the media, and the portions of the crystal that become internal during this process do not change after crystallization if kept at constant temp and pressure.
In contrast, if you put a plant and its media (soil, air, water) into constant temp and pressure, the plant will continue to grow and change until it exhausts the media. (assuming the temp and pressure are conducive to life) Ultimately plants become their own media by decomposing into soil.
If an external disturbance scatters the atoms inside the crystal, they will snap back to the lattice again. In a way similar (up to a point) to "normal" living organism's homeostasis.
You know that kind of reduction isn't the same thing.
Earth+Life is a different entity than Earth on its own, or any other planet.
Earth allows and protects life, and life in turn influences Earth. That kind of symbiosis on such a scale is in a class of its own, with no other equivalent or analogy that we know of. It deserves a special classification.
It seems nonsensical in any case to claim something that contains life among its constituent parts is not itself alive. Plenty of organisms have 'dead' tissue as part of their gestalt and no one thinks of them as 'mostly' alive.
http://www.bbc.co.uk/earth/story/20160823-the-idea-that-life...
> Cairns-Smith found a more eager audience in science journalists and the popular press. Other scientists showed interest, too: the evolutionary biologist and writer Richard Dawkins discussed the crystals-as-genes hypothesis in his 1986 book The Blind Watchmaker.
[...]
> His aim was to find a system much simpler than modern life, but which had some of the crucial properties of a living system. He found an answer in an unlikely place: clays.